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CHAPTER 18

Organic

Chemistry

18.1. INTRODUCTION
Historically, the term organic chemistry has been associated with the study of compounds obtained from
plants and animals. However, about 175 years ago it was found that typical organic compounds could be prepared
in the laboratory without the use of any materials derived directly from living organisms. Indeed, today great
quantities of synthetic materials, having properties as desirable as, or more desirable than, those of natural
products, are produced commercially. These materials include fibers, perfumes, medicines, paints, pigments,
rubber, and building materials.
In modern terms, an organic compound is one that contains at least one carbon-to-carbon and/or carbon-
to-hydrogen bond. (Urea, thiourea, and a few other compounds that do not fit this description are considered to
be organic compounds.) In addition to carbon and hydrogen, the elements that are most likely to be present in
organic compounds are oxygen, nitrogen, phosphorus, sulfur, and the halogens (fluorine, chlorine, bromine, and
iodine). With just these few elements, literally millions of organic compounds are known, and thousands of new
compounds are synthesized every year.
That an entire branch of chemistry can be based on such a relatively small number of elements can be
attributed to the fact that carbon atoms have the ability to link together to form long chains, rings, and a variety
of combinations of branched chains and fused rings.
In this chapter, some basic concepts of organic chemistry will be described. The objectives of the discussions
will be to emphasize the systematic relationships that exist in simple cases. Extension of the concepts presented
will be left to more advanced texts.

18.2. BONDING IN ORGANIC COMPOUNDS
The elements that are commonly part of organic compounds are all located in the upper right corner of
the periodic table. They are all nonmetals. The bonds between atoms of these elements are essentially covalent.
(Some organic molecules may form ions; nevertheless, the bonds within each organic ion are covalent. For
−
example, the salt sodium acetate consists of sodium ions, Na , and acetate ions, C 2 H 3 O 2 . Despite its charge,
+
the bonds within the acetate ion are all covalent.)
The covalent bonding in organic compounds can be described by means of the electron dot notation (Chap. 5).
The carbon atoms has four electrons in its outermost shell:
C

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